1. Field of the Invention
The present invention generally relates to a control apparatus for an electric power generating plant, and more particularly to a control apparatus for a power plant in which electric power is generated by utilizing vapor or steam produced by a steam generator (e.g. a reactor vessel in the case of a boiling water reactor or BWR, a steam generator in the case of a pressurized water reactor or PWR, a boiler in the case of a thermal power plant and so forth).
2. Description of the Related Art
As a control apparatus for a nuclear power plant and especially for a BWR nuclear power plant, there has been known a one which is primarily designed for performing a smooth load following control by coordinating harmonically the power control of the nuclear reactor with the generator output control in response to a demand for a relatively small and rapid change in the load of an associated power system, as is disclosed, for example, in Japanese Unexamined Patent Publication No. 131799/1980. According to this prior proposal, a load change demand signal produced by a turbine speed controller in correspondence to a change in frequency of the power system is added to a total steam flow demand signal produced by a pressure controller for thereby responding rapidly to the load change demand of the power system while controlling the reactor pressure to be stable. It is considered that this control approach can ensure improved power responsive control characteristics in the operation control system for the existing BWR nuclear power plant which is primarily directed to the power control of the nuclear reactor.
In the future, however, it is expected that the necessity will arise for such an operation control system which is designed primarily for the maintenance of the system frequency as the nuclear power plant occupies increasingly a greater proportion of the power supply source in the power system. In that case, a so-called governor-free operation will be required in which the generator output (turbine speed) is directly controlled as a function of change or variation in the frequency of the power system connected to the generator. In the governor-free operation, the steam flow control valve for controlling the steam flow fed to the turbine does not participate in the pressure control operation for suppressing fluctuation in the reactor pressure so far as magnitude of such fluctuation remains within a permissible range but performs the control operation only for the fluctuation of the turbine speed, i.e. the change in the system frequency. In this connection, it is noted that the control system according to the prior proposal mentioned above exhibits the control characteristics in which the change or fluctuation in the reactor pressure is always reflected and thus the response speed of this system is considered to be very low when compared with the response speed attained with the aforementioned governor-free operation.